The CAS Registry Mumber 203524-31-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 2,0,3,5,2 and 4 respectively; the second part has 2 digits, 3 and 1 respectively. Calculate Digit Verification of CAS Registry Number 203524-31: (8*2)+(7*0)+(6*3)+(5*5)+(4*2)+(3*4)+(2*3)+(1*1)=86 86 % 10 = 6 So 203524-31-6 is a valid CAS Registry Number.